Brilliant and Foolproof
by LadyChocolateLover
Summary: The Marauders, everybody knows, are very proud of their pranks. But, to pull a great prank, a brilliant and foolproof prank, you need seven phases and a bit of magic. OneShot.


**Disclaimer: Harry Potter belongs to J. K. Rowling.**

 _Special thanks to wonderful_ _Gaeleria_ _for betaing this for me, and also to_ _olivieblake_ _for her explanations on proper dialogue punctuation._

 _[This fic is a translation from Spanish of my own fic_ _ **Brillante e infalible**_ _]_

* * *

 **BRILLIANT AND FOOLPROOF**

 **OneShot**

 **Phase one: Think** **of** **a master plan**

Sirius Black sighed and turned on his bed. And then he turned again. And again. And then he turned once more.

"James," he hissed, turning a bit onto his right side.

"Mmmmwhat," James answered from the bed next to him.

"Are you sleeping?"

James didn't answer, but let out a sleepy murmur instead.

"Remus," Sirius whispered, this time to his left side.

"Sleep, Padfoot."

"I'm too bored, I can't sleep."

"Sirius," Remus sighed.

"What?"

"Do you know you're acting as if you are six instead of sixteen?"

"I don't care. I can't sleep."

"Ok, let's do something: if you stay quiet all night, I'll do your homework for a whole week," Remus sleepily promised.

"Done."

Five minutes and ten turns on the bed later, Sirius turned towards Remus again.

"Remus," he whispered.

"What," Remus answered, nearly fully asleep.

"I give up. I'm too bored to stay quiet," Sirius said, before adding, "but hey, if you still wanna' do my homework for a week, then feel free."

Remus sighed again. "I knew it."

"You knew what?"

"That you'd be unable to use our deal to think a brilliant prank and, at the same time, make me do your homework."

"Are you seriously telling me that you thought I would plan a new prank while I was quiet?"

"Of course. You're a Marauder, aren't you?"

Sirius felt his pride run away from him and throw itself on a wandless free fall from the window.

"I'm gonna' make you eat your words, Moony. This night I'm going to think of the best prank Hogwarts has ever seen, you'll see."

"And will it be brilliant and foolproof?"

"All that and a lot more," Sirius nodded.

"Well then, but do it in silence."

Sirius didn't answer, too busy thinking up a prank that wouldn't result in too harsh a punishment.

"Remus."

"What now?" he sighed.

"You're still doing my homework for a week, right?"

Peter's snore, two beds away, left the answer clear.

* * *

 **Phase two: Brag about your master plan before sharing it**

Sirius had been weirdly calm and wearing a smug smile all day, and Remus was starting to get scared.

"Sirius, are you okay?" Peter asked, looking at him with curiosity.

"I couldn't be better, my dear Wormtail," he answered, putting his bag on his shoulder and looking at the time. "We're going to be late for class."

James and Peter looked at him as if he suddenly had two heads.

"You sure you're okay?" Peter asked again. "We've got Transfiguration now."

"I'm perfectly fine, Peter. Come on, move, or else Minnie will have our heads if we're late again," he repeated. Remus feared the worst.

On the way to class, Sirius joked three times about Snape, flirted with a sixth-year Ravenclaw girl and jumped on James to be carried for a while.

"Good afternoon, Professor. You look more beautiful than you normally do," he greeted.

Surprisingly, they were within the first ones to arrive.

"Good afternoon, Mr. Black." Minerva looked at her watch, awed. When she confirmed that, effectively, they were on time, she gestured for them to enter. "Potter. Lupin. Pettigrew. It seems that at last you've learned the importance of punctuality," she commented, observing how they sat down.

"See the extreme measures we have to undertake to make you happy, Professor," Sirius answered, taking out a small piece of parchment while waving at the arriving students.

"And to think that you repay us with punishments..." James said, shaking his head and taking out a quill and ink. Then he winked at Lily Evans.

The bell rang, and Minerva closed the door with a with a wave of her wand.

"Now that we're all here, we'll start studying Human Transfiguration. Open your books to page 245 and carefully read the next ten pages. Then I want you to write a diagram, a summary and an essay explaining the basic theory, to be handed in at the end of the class. Make sure you understand the theory correctly, because tomorrow we'll start practising. If you have any doubts, you can ask me."

The students began to open their books and take out their materials, sighing.

"Professor," Sirius, who only had on the table a quill, some ink and the textbook, called.

"Tell me, Mr. Black."

"Can James and I write you an essay?"

"Of course you can. What's more, you must." The teacher peered over her spectacles at them from the other side of the class. "You and Mr. Potter have to write me an essay, diagram, and a summary, Mr. Black. Or weren't you listening?"

"Thank you, Professor. It was only a doubt I had."

Immediatly, Sirius took out a new piece of parchment.

"Prongs, you write the summary, I write the diagram, and we both write the essay," he murmured to James.

"Deal."

Remus rolled his eyes and turned to them. "You have to write the three things each."

"Minnie said _we_ could do them," Sirius argued while James nodded seriously.

Peter turned too, smiling. "Technically, Sirius' right."

"By the way, Remus, I've got the idea for you-know-what," Sirius muttered, bending forwards. "But we have to get detention first."

"You want to start on detention what will no doubt end on detention?" Remus asked.

"Yes."

"What are we starting?" Peter turned himself completely in his chair so he could see James and Sirius properly.

"Yeah, yeah. Why do we need to get detention again? We've been all week without, Sirius, we were going to break a record," James said, putting his quill on the table and looking at his friend with interest.

"Misters Pettigrew, Potter, Black, and Lupin, is something the matter?" Minerva asked sarcastically.

"No, Professor," James answered, smiling innocently.

"Then, if you may, please get back to work."

"Yes, Professor," the four answered at the same time.

Ten minutes later, Sirius scribbled a note on the small piece of parchment, showed it to James, and then hit Remus on the back.

"What do you want, Sirius?" the lycanthrope asked, turning to him.

Sirius gave him the piece of parchment, perfectly folded, and a quill.

"Here, I've just remembered that this quill is yours," he said, pretending under the teacher's inquiring glance.

"Ah, thanks," Remus answered, always kind.

He unfolded the note on the middle the desk, and he and Peter joined their heads together to read it, while, in the back tables, Sirius and James whispered.

 _I've got a foolproof plan._

 _Let's meet_ _at_ _the Shack at half past ten tonight. Moony, ask Lily to do your rounds tonight._

 _And someone please explain_ _to_ _me the four Transfiguration laws._

No one noticed the curious glance Minerva McGonagall threw at them.

* * *

 **Phase three: Revise the details before starting the plan (again, master plan)**

"Remus, it's my prank," Sirius protested. "And if I say that it has to start while on detention, then it has to start while on detention."

"I'm just saying that it's not a good idea."

"Honestly, to send the letter we don't really need to be on detention," James reasoned.

"And then, how do you propose we leave the letter in her private office, which we only have access to while on detention?" Sirius countered, stealing a chocolate frog from Remus.

"I can do it," Peter suggested, and reddened when they all glanced in his direction. "I can transform myself into a rat and sneak in through the window or something."

"Yeah," Sirius nodded. "We can carry you until we're near the office so you don't have to worry about carrying the letter and avoiding Mrs. Norris at the same time."

"It's a good idea, Wormtail," James said, smiling.

"And who writes the letter?" Remus asked, gifting Peter with a chocolate frog.

"You write it, and then we distort the handwriting with magic," James proposed.

"All right," Remus sighed. "Pass me a quill and parchment," he added, while transforming a loose board into a table and a rock into a chair.

Peter got out of his backpack a quill, some ink, and a piece of parchment, and passed them to Remus who, already seated, was looking expectantly at Sirius.

"All right, dictate," he said, wetting the quill in the ink.

"Dear Professor Minerva McGonagall," Sirius started, walking around the room and waving his arms. "Comma. I see myself in the regrettable labour of informing you that your methods of teaching do not comply with the criteria established by the (look out, they're initials) U. M. I. E., the Union for Magical International Education. Period."

"For that reason," James continued, "comma, you must undertake an owl course to learn to educate this generation of witches and wizards, comma, which is not like the last generation of witches and wizards nor like the next generation of witches and wizards. Period."

Sirius nodded seriously, and Remus had to contain his laughter.

"Your turn, Peter."

"Oh, me?"

"Of course, it's a paragraph each," Sirius answered, already seated on the floor. "Do delight us."

"Where were we?" Peter asked.

"The owl course," Remus answered, wetting the quill again.

"Okay," Peter sighed. "Copy: said course will arrive tomorrow morning, comma, and you only have to memorize it to put it into action as soon as possible to educate correctly this generation of witches and wizards. Full stop. Of course, comma, you may send any doubt you have with an owl, and we will answer joyfully. Period."

James laughed.

"Your turn, Moony," Sirius said, grinning.

Remus wrote something on the parchment before murmuring a spell to change the handwriting.

"Done."

"Read it," Sirius complained.

"Without further ado, comma, I salute you, full stop. I hope you enjoy our course and learn to teach the witches and wizards of this generation correctly, which will take us to the future and to progress. Period. May everything you teach be useful and everything your students learn help them in life. Period. Yours faithfully, comma, Laudinus Parexis, comma, Subsecretary of the U. M. I. E.

Postscript: If you do not comply with the owl course, comma, there will be consequences, comma, Professor McGonagall, comma, there will be consequences. Ellipsis."

They all laughed happily.

"Minnie will never buy this," James commented while Remus put the parchment in an envelope and sealed it.

"That's the joke," Sirius answered. "C'me on, let's go leave her the letter before going to sleep."

The quartet went out the door ready to make a prank that could cost them dearly, but none of them faltered.

They were Gryffindors through and through.

* * *

 **Phase four: Observe the results of the first part of the master plan and commence the second part**

"Hey, Albus," Professor McGonagall's voice said.

Sirius stopped suddenly and both he and Peter hid behind a statue.

"Yes?"

"Have you ever heard of the U. M. I. E.?"

Peter giggled and looked at Sirius with round eyes, who returned an equally surprised look.

"No, I don't think I've ever heard of it, Minerva. Why?" the old director answered.

Minerva sighed, exasperated. "Just what I thought. I've received a letter from that organization that says my educational methods aren't correct."

"Don't worry, Minerva, you couldn't be a better teacher. That must be a prank."

"Well, if I catch the pranksters..." murmured Minerva, and the footsteps of both Professors moved away on the other direction.

Sirius looked at Peter and grinned happily.

"Let's finish this, okay?" he asked. Peter nodded, smiling, and both started to run towards the Transfiguration class.

When they arrived, Peter stayed guarding at the door, while Sirius entered running, waved his wand and wrote some words on the blackboard.

 _It's hard to believe that at your age you still have doubts about your teaching quality, Professor McGonagall._

"Did you just call her old?" Peter asked from his position.

Sirius looked at the blackboard and waved his wand again.

"Probably."

* * *

 **Phase five: Relax and enjoy the absolute triumph of the master plan, which will be remembered forever**

"Good morning, Minnie," Sirius said, entering the Transfiguration class, again on time and again followed by the rest of the Marauders.

"Hi."

"Morning..."

"How are you?"

The few students who had already arrived were too busy observing attentively the words on the blackboard to be amazed at the arrival of the Marauders, but Professor McGonagall looked at them with attention.

"Good morning. Are you ill, sirs, for you have come two consecutive days on time to my class?"

"Not at all, Professor," James answered while seating. "It's just that we wanted to see you and by arriving late we don't get anything."

Minerva glanced at him sceptically, but said nothing.

Meanwhile, the rest of the class had already arrived and been seated, and each and every one of the students were looking attentively at the words on the blackboard.

"I suppose that nobody knows anything about this," the teacher said, pointing at the blackboard with her wand.

All the students looked automatically at the Marauders, who looked back at them calmly.

No one said anything.

"I see. Well, let's ignore it –that means we're not going to look at it, Miss McDonald, so please pay attention to me; and let's continue with Human Transfiguration."

Suddenly, the blackboard started to vibrate and a light came off it.

All the attention was directed there and the whole class observed, astonished, how the letters disappeared and other ones appeared on their place.

 _Yesterday, we made a letter arrive for Professor McGonagall, which said that she didn't comply with the educational criteria of the Union for Magical International Education and that she would have to re-educate herself via an owl course._

All the students inhaled abruptly and looked at the Professor before turning their attention to the blackboard, where another sentence was written.

 _Of course, it's a lie._

 _Professor McGonagall is,_ _without a doubt, the best teacher of the w_ _hole school: strict but fair, she explains her lessons in an unbeatable way and she loves her students dearly (even though sometimes it doesn't look like it.)_

Sirius elbowed James, and both observed Minerva's blush and her smile while she looked at the blackboard.

 _While it hurts that at first she thought she wasn't teaching us correctly, we know she soon recovered her reason and her faith in her educational ways (namely, never-ending essays and exercises, even longer explanations, whole classes dedicated to_ _practising the theory, and absolute freedom to ask any type of question at all ti_ _mes.)_

 _Never doubt yourself, Professor, because you're better than triple-chocolate cake._

 _Happy birthday, Minnie._

 _We love you._

The whole class cheered, and Minerva wiped a tear discretely.

"Happy birthday, Professor!" Sirius shouted, while James got on a chair.

"Everybody: sing!" he screamed, before starting to move his wand like an orchestra director. "Happy birthday to you..."

"Happy birthday to you, happy birthday Professor, happy birthday to you...!" they all sang –even Lily Evans, before cheering again.

Remus transfigured Sirius' quill into a bouquet of flowers and approached the platform to give them to Minerva, who was blowing her nose, touched.

"Happy birthday, Professor," he said.

"Thank you," Minerva inhaled and accepted the flowers before sending Remus to his seat. "Thank you, really. I wasn't expecting this at all, and I am very thankful for this detail, even though I suppose you know I'm going to punish you," she added, looking at the Marauders, who just shrugged. "Now, please open your books on page 250, take out your wands and start exercise one."

* * *

 **Phase six: Accept the master's plan's consequences, because Professor McGonagall makes no exceptions**

"Sirs, I have no words," Minerva said while sitting in her office.

After her, the Marauders entered and sat comfortably on the chairs just opposite the desk.

"We wanted to gift you with something beautiful for your birthday, Minnie," Sirius answered.

"And wouldn't it have been easier to just give me some flowers instead of making all that show in my class?"

"Probably," James answered, "but then you wouldn't have liked it half as much, admit it."

"What's more, if we hadn't done it, then you wouldn't have a motive to punish us," Peter added.

"That's true. And don't deny it, you're going to punish us," Sirius accused, smiling through all.

Minerva grinned. "I'm going to punish you even though I have really appreciated the detail, sirs."

"But please be good, Minnie, for we've done it with love," James begged.

"For that reason, I'm not going to deduct House points," the teacher answered, looking at them over her glasses. "Let's see: you've sent a letter as if you were an official organization to scare a teacher, you've spelled the blackboard on the Transfiguration class, you've stopped the normal execution of class, and you've created a nice scandal.

For all that, you'll understand that I'm putting you in charge of the cleaning and the order of all the classrooms on the second floor for a whole week."

"All right," Remus nodded.

"Good night, sirs."

The Marauders got up and started walking towards the exit.

"Oh, by the way," the teacher added, stopping them all at the door. "Mister Black and Mister Potter, I'd thank you if you explained to me why do I have one's diagram, the other's summary and an essay signed as 'From your studious students, James Potter and Sirius Black'."

"Well, I asked you if James and I could do the essay and you answered that, in fact, we had to do the essay," Sirius shrugged with a smug smile. "So that's what we did. We did an essay."

"All right. And do I have to divide the essay's mark and give half of it to each one of you?"

"Sirius and I'd be very thankful if you gave each of us the whole mark, Professor," James answered.

"No doubt. And I'd be very thankful, Mister Potter, if when I ask for a diagram, a summary and an essay you gave me all three of them and not a summary and, it seems, half of an essay."

James had the decency to look chastised, but Sirius remained perfectly composed.

"And can any of you explain why you decided to tergiversate my words and do what you wanted by dividing the work?"

"Because unity makes strength, Minnie, and James and I united for an Outstanding," Sirius answered, winking at her.

Minerva touched her temple with her fingers. "I'm not going to punish you for this, but make sure that for tomorrow you have written everything."

"Yes, Professor," James and Sirius answered together.

"You may go."

When Remus had opened the door and they all were ready to leave, Minerva stopped them again.

"Sirs."

"Professor," Peter answered.

"Know that I too appreciate you, but if you ever make a show like this again, I'm going to rethink it."

"Understood, Professor," Remus answered.

Immediately after, the four Marauders disappeared through the door, and Minerva was left alone, thinking.

* * *

 **Phase seven: Repeat to death since phase one**

James Potter sighed and turned on his bed. And then he turned again. And again. And then he turned once more.

In the end, he turned onto his left side.

"Sirius," he whispered.

"Mmmmwhat," he mumbled.

"I can't sleep."

Sirius sighed. "And why should I care?"

"Guys, shut up," muttered Peter from his bed, nearly fully asleep.

"I don't know what to do," James continued, ignoring Peter, "and I thought that you may have some ideas."

"Let's see, Prongs. You have Marauder spirit, right?"

"Of course," James answered, offended.

"And what have we been trying to do since we started school and haven't been able to do yet?"

"Become legendary?"

"We already are."

"Have Snivellus expelled?"

"Apart from that."

James was quiet for so long Sirius thought he was asleep.

"I don't know," James admitted in the end.

"Prank Minnie and survive without detention."

"Okay. All right. So what?"

"Well, using your Marauder spirit and your insomnia, you could think of a brilliant and foolproof prank."

"Fuck, that's right. I'm gonna' think of a brilliant and foolproof prank."

"Let's see if that's true and lives up to my expectations."

James stuck out his tongue in the dark.

"It will surpass them, Padfoot, it will surpass them."

* * *

 **Final phase: Hope Minerva McGonagall doesn't punish anyone for the possible consequences of the master plan**

[Misters Moony, Wormtail, Padfoot, and Prongs regret to inform they have never reached such a high level as the final phase.]

* * *

 _So, what did you think? Drop me a review and let me know! :)_

 _LadyChocolateLover_


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